Noise/vibration reduction control

ABSTRACT

Systems and methods for reducing noise or vibration generated by an internal combustion engine are described. An engine controller is arranged to operate the working chambers of the engine in a cylinder output level modulation manner A noise/vibration reduction unit actively control of a device that is not a part of the powertrain. The device is controlled in a feed forward manner to alter an NVH characteristic of the vehicle in a desired manner based at least in part on a characteristic of the cylinder output level modulation operation of the engine.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/894,548, filed on Feb. 12, 2018. U.S. application Ser. No. 15/894,548is a Continuation-in-Part of U.S. application Ser. No. 15/485,000 (nowU.S. Pat. No. 10,072,592), filed Apr. 11, 2017, which is a Continuationof U.S. application Ser. No. 15/274,029 (now U.S. Pat. No. 9,689,328),filed Sep. 23, 2016, which is a Divisional of U.S. application Ser. No.15/180,332 (now U.S. Pat. No. 9,476,373), filed Jun. 13, 2016. U.S.application Ser. No. 15/180,332 is a Divisional of U.S. application Ser.No. 14/919,011 (now U.S. Pat. No. 9,399,964), filed Oct. 21, 2015, whichclaims priority to U.S. Provisional Application Nos.: 62/077,439, filedNov. 10, 2014; 62/117,426, filed Feb. 17, 2015; and 62/121,374, filedFeb. 26, 2015. Each of these priority applications is incorporatedherein in its entirety.

The present Application and U.S. application Ser. No. 15/894,548 arealso Continuation-in-Parts of U.S. application Ser. No. 14/509,792,filed Oct. 8, 2014, which claims priority of U.S. ProvisionalApplication No. 61/888,935, filed Oct. 9, 2013, each of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to methods and mechanisms forreducing noise and vibration generated by internal combustion engines.Various embodiments involve noise, vibration and/or harshness (NVH)reduction in cylinder output level modulation engine control.

BACKGROUND

Most vehicles in operation today are powered by internal combustion (IC)engines. Internal combustion engines typically have multiple cylindersor other working chambers where combustion occurs. The power generatedby the engine depends on the amount of fuel and air that is delivered toeach working chamber.

The combustion process and the firing of cylinders can introduceunwanted noise, vibration and harshness (NVH). For example, the enginecan transfer vibration to the body of the vehicle, where it may beperceived by vehicle occupants. Sounds may also be transmitted throughthe chassis into the cabin of the vehicle. Under certain operatingconditions, the firing of cylinders generates undesirable acousticeffects through the exhaust system and tailpipe. Vehicle occupants maythus experience undesirable NVH from structurally transmitted vibrationsor sounds transmitted through the air.

There are a wide variety of ways to improve the acoustic and vibrationcharacteristics of a vehicle. Typically, vehicles utilize engine mountsthat both support the engine and absorb vibration from the engine. Insome vehicles, the engine mount is active e.g., it can be stiffened ormade more compliant depending on the engine speed and other conditions.For example, when the engine is at idle or under low load conditions,the active mount may become more compliant so that the vibration isbetter absorbed. At higher speeds, however, the mount may be stiffenedto prevent excessive engine motion from damaging the connections betweenthe engine and its attached components.

Some vehicles use a passive exhaust valve to help reduce engine noise.For example, the exhaust valve may involve a flap that is situated nearthe tailpipe along a line that connects the exhaust ports of thecylinders to the tailpipe. The flapper valve impedes the exhaust flowfrom the cylinders to the tailpipe. If the exhaust flow rate is low, theflap may tend to close, while high exhaust flow rates force the flap toopen more widely. The flapper valve helps to dampen, reflect, ormodulate pressure waves in the exhaust path that are generated by theengine, thereby reducing undesirable acoustic effects.

To help improve passenger comfort and reduce undesirable sounds in thecabin of a vehicle, an active noise cancellation system may be used. Insome vehicles, for example, there are one or more speakers andmicrophones situated within the cabin. When noises from the road, engineor other parts of the vehicle enter the cabin, the microphones detectthe noise. The noise is analyzed and used to generate canceling soundsthrough the speakers. The amplitude, phase, frequency and wavelength ofthe generated sound waves are selected to cancel the undesirableacoustic effects.

Fuel efficiency of many types of internal combustion engines can besubstantially improved by varying the displacement of the engine. Thisallows for the full torque to be available when required, yet cansignificantly reduce pumping losses and improve thermodynamic efficiencythrough the use of a smaller displacement when full torque is notrequired. The most common method of varying the displacement today isdeactivating a group of cylinders substantially simultaneously. In thisapproach no fuel is delivered to the deactivated cylinders and theirassociated intake and exhaust valves are kept closed as long as thecylinders remain deactivated.

Another engine control approach that varies the effective displacementof an engine is referred to as “skip fire” engine control. In general,skip fire engine control contemplates selectively skipping the firing ofcertain cylinders during selected firing opportunities. Thus, aparticular cylinder may be fired during one engine cycle and then may beskipped during the next engine cycle and then selectively skipped orfired during the next. Skip fire engine operation is distinguished fromconventional variable displacement engine control in which a designatedset of cylinders are deactivated substantially simultaneously and remaindeactivated as long as the engine remains in the same variabledisplacement mode. Thus, the sequence of specific cylinders firings willalways be exactly the same for each engine cycle during operation in avariable displacement mode (so long as the engine remains in the samedisplacement mode), whereas that is often not the case during skip fireoperation. For example, an 8 cylinder variable displacement engine maydeactivate half of the cylinders (i.e. 4 cylinders) so that it isoperating using only the remaining 4 cylinders. Commercially availablevariable displacement engines available today typically support only twoor at most three fixed displacement modes.

In general, skip fire engine operation facilitates finer control of theeffective engine displacement than is possible using a conventionalvariable displacement approach. For example, firing every third cylinderin a 4 cylinder engine would provide an effective displacement of ⅓^(rd)of the full engine displacement, which is a fractional displacement thatis not obtainable by simply deactivating a set of cylinders.Conceptually, virtually any effective displacement can be obtained usingskip fire control, although in practice most implementations restrictoperation to a set of available firing fractions, sequences or patterns.

Many skip fire controllers are arranged to provide a set of availablefiring patterns, sequences or firing fractions. In some circumstancesthe set of available firing patterns or fractions will vary as afunction of various operating parameters such as engine load, enginespeed and transmission gear. Typically the available firing patterns areselected, in part, based on their NVH characteristics. Transitionsbetween firing fraction levels must be managed to avoid unacceptable NVHduring the transition. In particular, changes in the firing fractionmust be coordinated with other engine actuators to achieve smooth firingfraction transitions.

The Applicant, Tula Technology, Inc., has filed a number of patentsdescribing various approaches to skip fire control. By way of example,U.S. Pat. Nos. 8,099,224; 8,464,690; 8,651,091; 8,839,766; 8,869,773;9,020,735; 9,086,020; 9,120,478; 9,175,613; 9,200,575; 9,200,587;9,291,106; 9,399,964, and others describe a variety of enginecontrollers that make it practical to operate a wide variety of internalcombustion engines in a dynamic skip fire operational mode. Each ofthese patents and patent applications is incorporated herein byreference.

In some applications referred to as multi-level skip fire, individualworking cycles that are fired may be purposely operated at differentcylinder outputs levels—that is, using purposefully different air chargeand corresponding fueling levels. By way of example, U.S. Pat. No.9,399,964 (which is incorporated herein by reference) describes somesuch approaches. The individual cylinder control concepts used indynamic skip fire can also be applied to dynamic multi-charge levelengine operation in which all cylinders are fired, but individualworking cycles are purposely operated at different cylinder outputlevels. Dynamic skip fire and dynamic multi-charge level engineoperation may collectively be considered different types of cylinderoutput level modulation engine operation in which the output of eachworking cycle (e.g., skip/fire, high/low, skip/high/low, etc.) isdynamically determined during operation of the engine, typically on anindividual cylinder working cycle by working cycle (firing opportunityby firing opportunity) basis. Three level (high, low, skip) cylinderoutput level modulation control may be characterized by a firingfraction (FF), which is the fraction of fired firing opportunities tototal firing opportunities, and a level fraction (LF), which is theratio of high firings to total firings. An effective firing fraction(EFF) can be determined as EFF=FF*LF+FF*R*(1−LF), where R is the ratioof the low firing output to the high firing output.

It should be appreciated that cylinder output level engine operation isdifferent than conventional variable displacement in which when theengine enters a reduced displacement operational state, a defined set ofcylinders are operated in generally the same manner until the enginetransitions to a different operational state.

SUMMARY OF THE INVENTION

A variety of methods and arrangements are described for reducingvibration or noise generated from an internal combustion engine duringskip fire or other cylinder output level modulation operation. In someembodiments, a device that is not a part of the powertrain is activelycontrolled in a feed forward manner to alter the NVH characteristics ofthe vehicle in a desired manner based at least in part on one or moreskip fire characteristics. In some embodiments specific working chamberoutput level decisions are used in the active feed forward control ofthe device such that the device is controlled differently during theassociated firing opportunity based on the associated output leveldecision. In other embodiments, a firing characteristic associated withthe cylinder output level modulation is used in the feed forwardcontrol. In various embodiments, the firing characteristic used in thefeed forward control includes one of: a current operating firingfraction; a firing frequency engine order or a harmonic thereof; aminimum repeating pattern length; a denominator of the firing fraction;or a parameter indicative of any of the foregoing.

In some embodiments, at least two filters are used in the active controlof the device. In some such embodiments, a first one of the filters maybe used in association with skipped firing opportunities and not used inassociation with fired firing opportunities. Conversely, the second oneof the filters is used in association with fired firing opportunitiesand is not used in association with the skipped firing opportunities.More generally, when cylinders are arranged to operate at differentfiring levels, different filters may be used in association with firingsat the different levels.

In some embodiments that utilize specific firing decisions in thecontrol of the device, for each fired working cycle, the actuation ofthe device is substantially synchronized with the firing impulse (orlack thereof in skipped working cycles).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the advantages thereof, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1A is a block diagram of an engine controller and a noise/vibrationreduction unit according to a particular embodiment of the presentinvention.

FIG. 1B is a representative pattern of acoustic pressure waves emanatingfrom a vehicle tailpipe.

FIG. 2A is a diagram of an engine exhaust system and a flow regulatorcontrol system according to a particular embodiment of the presentinvention.

FIG. 2B is a diagram of a flow regulator according to a particularembodiment of the present invention.

FIG. 3A is a flow diagram illustrating an active mount control systemaccording to a particular embodiment of the present invention.

FIG. 3B is a flow diagram illustrating the location of two types ofactive mounts according to a particular embodiment of the presentinvention.

FIG. 3C is a diagram illustrating active engine mounts and active enginesub-frame to frame mounts according to a particular embodiment of thepresent invention.

FIG. 3D is a diagram illustrating an active exhaust hanger according toa particular embodiment of the present invention.

FIG. 4A is a flow diagram illustrating an active noise cancellationcontrol system according to a particular embodiment of the presentinvention.

FIG. 4B is a flow diagram illustrating two example control paths for anactive noise cancellation control system.

FIG. 4C is a flow diagram illustrating an active noise cancellationcontroller with a finite response filter according to a particularembodiment of the present invention.

FIG. 5A is a flow diagram of a vibration damper control system accordingto a particular embodiment of the present invention.

FIG. 5B is a diagram of a vibration damper incorporated into a vehicleaccording to a particular embodiment of the present invention.

FIG. 6 is a diagram illustrating an active vibration control systemaccording to a particular embodiment.

FIG. 7A is a diagram illustrating a calibrated, feed-forward acousticmanagement system.

FIG. 7B is a diagram illustrating an adaptive feed-forward acousticmanagement system.

FIG. 8 is a diagram illustrating a powertrain having a variable rateabsorber and an absorber controller for controlling the absorptionfrequency of the variable rate absorber.

FIG. 9 is a table illustrating the determination of the minimumrepeating pattern length for various combinations of firing fraction andlevel fraction.

In the drawings, like reference numerals are sometimes used to designatelike structural elements. It should also be appreciated that thedepictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION

The present invention relates generally to methods and mechanisms forreducing noise, vibration and harshness (NVH) generated by an internalcombustion engine. The firing impulse arising from the combustion eventand associated motion of the intake and exhaust valves generates bothacoustic noise and vibrations. The NVH may have both a radiatedcomponent, which is transmitted through the air, and a structure-bornecomponent, which is transmitted through the vehicle. More specifically,various implementations involve using known firing information in a skipfire or other cylinder output level modulation engine control system toreduce NVH. The firing information may include individual skip/firedecisions; individual firing level decisions; firing density/firingfraction related information; known firing sequences; firing order; etc.

In dynamic skip fire engine control system, each working chamber is notnecessarily fired during every engine cycle. Instead, one or moreselected working cycles of one or more working chambers are deactivatedand one or more selected working cycles of one or more working chambersare fired. Individual working chambers are sometimes deactivated andsometimes fired. In various skip fire applications, individual workingchambers have firing sequences that can change on a firing opportunityby firing opportunity basis. For example, an individual working chambercould be skipped during one firing opportunity, fired during the nextfiring opportunity, and then skipped or fired at the very next firingopportunity.

The operation of each working chamber is therefore quite different fromthe operation of a working chamber in a more conventional engine, inwhich each working chamber is steadily fired; for example, once everytwo engine revolutions for a 4 stroke engine. Because skip fire enginecontrol can involve different working chambers with different firingsequences, there is a greater likelihood that low frequency, alternatingfiring patterns may be generated. Such firing patterns tend to produceundesirable acoustic effects.

An advantage of some skip fire engine approaches, however, is thatinformation about future firing decisions are known before the firingsactually take place. Various implementations of the present inventiontake advantage of this feature. More specifically, firing information isused in a wide variety of ways to reduce undesirable noise andvibration. For example, a firing fraction, firing order, firingsequence, firing sequence phase information or a firing decision for oneor more working chambers may be used to control an active mount system,a variable rate absorber, an active noise cancellation system, anexhaust flow regulator/valve, a vibration damper, an active exhausthanger and/or any of a variety of other types of dampers or mounts.

Referring initially to FIG. 1A, an engine controller 100 according to aparticular embodiment of the present invention will be described. Theengine controller 100 includes a firing fraction calculator 112, afiring timing determination module 120 and an engine control unit 140.The engine controller 100 communicates with a noise/vibration reductionunit 102 and an engine 110. The noise/vibration reduction unit 102 sendsappropriate signals to the various actuators; i.e. engine mounts,exhaust flapper, cabin speakers, etc., to reduce the NVH experienced byvehicle occupants.

Initially, the firing fraction calculator 112 receives an input signalthat is treated as a request for a desired engine output. The signal maybe derived from a pedal position sensor (PPS) or any other suitablesource, such as a cruise controller, an ECU, a torque calculator, etc.In some implementations, there may be an optional preprocessor thatmodifies the input signal prior to delivery to the firing fractioncalculator, for example, to account for auxiliary device loads.

The firing fraction calculator 112 receives the input signal and isarranged to determine a skip fire firing fraction that would beappropriate to deliver the desired output under selected operatingconditions. The firing fraction is indicative of the fraction orpercentage of firings under the current (or directed) operatingconditions that are required to deliver the desired output. In somepreferred embodiments, the firing fraction may be determined based onthe percentage of optimized firings that are required to deliver thedriver requested engine torque (e.g., when the cylinders are firing atan operating point substantially optimized for fuel efficiency).However, in other instances, different level reference firings, firingsoptimized for factors other than fuel efficiency, the current enginesettings, etc. may be used in determining the appropriate firingfraction. It should be appreciated that a firing fraction may beconveyed or represented in a wide variety of ways. For example, thefiring fraction may take the form of a firing pattern, sequence or anyother firing characteristic that involves or inherently conveys theaforementioned percentage of firings. The firing fraction calculatorgenerates a commanded firing fraction 113, which is received by thefiring timing determination module 120 and the noise/vibration reductionunit 102.

The firing timing determination module 120 is arranged to issue asequence of firing commands (e.g., drive pulse signal 115) that causethe engine to deliver the percentage of firings dictated by thecommanded firing fraction 113. The firing timing determining module 120may take a wide variety of different forms. By way of example, sigmadelta converters work well as the firing timing determining module. Thesequence of firing commands outputted by the firing timing determiningmodule 120 is passed to an engine control unit (ECU) 140 whichorchestrates the actual firings. The firing timing determination module120 is arranged to deliver a wide variety of firing information to thenoise/vibration reduction unit. This may include, but is not limited to,the drive pulse signal 115 or a firing sequence, a firing decision for aparticular working chamber, a signal indicating the number or identityof that working chamber, and/or the firing history of a selected workingchamber. In various applications, this information can be directly sentbetween the noise/vibration reduction unit 102 and the firing timingdetermination module 120 or the noise/vibration reduction unit 102 maybe able to infer this information. For example, if the firing timingdetermination module 120 sends a fire/skip signal to the noise/vibrationreduction unit 102 additional information on the cam position may besent over optional signal line 161. These two pieces of information, thefire/skip decision and the cam position would allow the noise/vibrationreduction unit 102 to determine which cylinder is being fired/skipped.

The noise/vibration reduction unit 102 is arranged to utilize firinginformation (e.g., a firing fraction, firing order, minimum repeatingpattern length, a drive pulse signal or firing sequence, firing sequencephase information, a firing decision (skip/fire; high/low;high/low/skip, etc.)), often in conjunction with the engine speed, tohelp reduce or eliminate NVH using a wide variety of differentapproaches. In the illustrated embodiment, for example, thenoise/vibration reduction unit may include a flow regulator controller160, an active mount controller 162, an active noise cancellation (ANC)controller 164, a vibration damper controller 166, an active vibrationcontroller (AVC) 167, and an active exhaust hanger controller 168. Thesecontrollers use the firing information to adjust operating parametersfor an exhaust valve/flow regulator, an active mount for the engine, anactive noise cancellation system, a damper vibration control system, anactive vibration controller system and an active exhaust hanger,respectively. For example, based on the firing information, the activemount may become more or less compliant and more or less damped, theflow regulator may be set to further allow or restrict exhaust flow, andthe ANC may be configured to emit particular sounds that cancel noisegenerated by the engine. Put another way, the firing informationindicates how one or more working chambers will be operated (e.g.,skipped or fired) and the noise/vibration reduction unit is arranged tohelp mitigate the NVH effects of such operations. In the illustratedembodiment, the NVH control is feed forward in nature, since it usesinformation concerning upcoming firings to adjust various actuators inthe noise/vibration reduction unit. In practice fire/skip decisions aregenerally made several firing opportunities, for example 3 to 10, priorto the engine executing the fire/skip command. In order to synchronizethe various NVH mitigation controllers with the actual engine operationa variable delay block 163 may be incorporated into the noise/vibrationreduction unit 102. Additional feedback elements may be added to the NVHcontrol as required. It should be appreciated that the present inventionis not limited to the above types of controllers and structures. Not allof these controllers, 160, 162, 164, 166, 167, and 168 need beincorporated into a vibration reduction unit 102. Only one or morecontrollers need be present and additional controllers may be present.

More generally, the noise/vibration reduction unit can be used tocontrol any suitable mechanism that reduces NVH based on the firinginformation. Generally, the present invention contemplates the use ofdynamic skip fire engine control. The assignee of the presentapplication has filed multiple patent applications on a wide variety ofskip fire and other engine designs, such as U.S. Pat. Nos. 7,954,474;7,886,715; 7,849,835; 7,577,511; 8,099,224; 8,131,445; and 8,131,447;U.S. patent application Ser. Nos. 13/774,134; 13/963,686; 13/953,615;13/953,615; 13/886,107; 13/963,759; 13/963,819; 13/961,701; 13/963,744;13/843,567; 13/794,157; 13/842,234; 13/004,839, 13/654,244 and13/004,844; and U.S. Provisional Patent Application Nos. 61/080,192,61/104,222, and 61/640,646, each of which is incorporated herein byreference in its entirety for all purposes. Many of the aforementionedapplications describe firing controllers, firing fraction calculators,filters, powertrain parameter adjusting modules, firing timingdetermining modules, and other mechanisms that may be integrated into orconnected with the engine controller 100 and the noise/vibrationreduction unit 102. In some cases the noise/vibration reduction unit 102may also be integrated into the engine controller 100.

Referring next to FIG. 1B, a representative pattern of the acousticpressure waves 150 emanating from a vehicle tailpipe will be described.The pressure wave is composed of a time varying pressure wave having aperiod T₁ frequency modulated by a lower frequency wave having a periodT₂. The period T₁ may be associated with the rate of cylinder firing.For example, for an 8 cylinder engine operating at 2000 rpm (revolutionsper minute) at a firing fraction of 0.33 the firing frequency is 44 Hzcorresponding to a period between successive cylinder firings (T₁) of22.7 milliseconds. The value of T₁ will obviously change depending onthe firing fraction, engine rpm, and number of cylinders. As describedin U.S. patent application Ser. No. 13/886,107 path length differencesin the exhaust system between the various cylinders can give rise tobeating effects as shown in FIG. 1B. The beating modulates the noiseemanating from the cylinder firings at a frequency T₂, where T₂ isgreater than T₁. A representative value for T₂ may be 250 milliseconds;however, higher or lower values may be present depending on the exhaustpath layout and engine operating characteristics. The systems describedbelow to actively cancel undesirable noise or vibration may be designedto lessen the perception of the acoustic pattern shown in FIG. 1B onvehicle occupants and individuals in the vicinity of the vehicle. Thepattern shown in FIG. 1B is representative only and these systems may bedesigned to compensate for other acoustic patterns and vibrations asdescribed below.

Referring next to FIG. 2A, a flow regulator control system 200 accordingto a particular embodiment of the present invention will be described.The flow regulator control system includes the engine controller 100 andthe flow regulator controller 160. The flow regulator controller 160communicates with and controls a flow regulator 202 situated in atailpipe 206 of a vehicle exhaust system 204.

The flow regulator 202 helps control the exhaust flow rate through aline 208 that connects the engine 110 to the tailpipe 206. The flowregulator 202 may take a wide variety of forms. One example of a flowregulator is shown in FIG. 2B. In the illustrated embodiment, the flowregulator 202 includes a flap 212 whose position can be adjusted tofurther restrict or allow exhaust flow. A variable spring may also beused to position and modify the damping characteristics of the flap 212.Some designs allow for a predetermined number of possible positions,each of which allows exhaust flow to a different degree. The control forthe flow regulator may be handled in any suitable manner (e.g.,pneumatically, electronically, etc.).

If properly calibrated, the flow regulator 202 can help reduceundesirable acoustic effects generated by skip fire engine control.These acoustic effects can be particularly problematic in a vehicle inwhich exhaust gases from different banks have different distances totravel to the tailpipe. To provide an illustrative example, consider theengine in FIG. 2A. The working chambers in this example are arranged intwo banks, a first bank 214 that includes working chambers 1, 3, 5 and 7and a second bank 216 that includes working chambers 2, 4, 6, 8. Eachbank is connected via a Y pipe to the tailpipe 206. Because of thearrangement of the banks and the exhaust system, exhaust from the firstbank 214 has a greater distance to travel to the tailpipe 206 thanexhaust from the second bank 216.

This type of arrangement can be problematic when certain fractions ofthe working chambers are fired. In particular, problems can occur whenfirings occur in one bank and then the other in an alternating, regularpattern. For example, consider a situation in which the engine is firedin the order 1-8-7-2-6-5-4-3 during all cylinder operation, i.e. afiring fraction of 1. If the firing fraction is ⅓ and involves firingevery third working chamber and skipping the next two working chambers,then the order of combustion events could be 2-4-8-6-3-7-5-1.

The combustion events for working chambers 3-7-5-1 are all from thefirst bank 214 and the other combustion events (2-4-8-6) are all fromthe second bank 216. In this situation, the engine alternates betweenfour firings on one bank and four firings on the other bank. The soundsgenerated by the first bank 214 are delayed relative to the second bank216 due to the different distances that the sounds need to traverse fromtheir respective banks to reach the end of the tailpipe. Thisarrangement can lead to low frequency, beating/modulating sound patternsas shown in FIG. 1B. These modulated patterns can be perceived asannoying by vehicle occupants.

Since particular firing fractions and engine arrangements are known togenerate certain problematic patterns, the flow regulator is arranged touse firing information to help reduce or eliminate acoustic effectsassociated with those patterns. By limiting the passage of pressurewaves emanating from the engine, the flow regulator, when properlycalibrated, can reduce or eliminate undesirable noise generated by thecombustion process. In the illustrated embodiment, for example, the flowregulator controller receives a firing fraction (e.g., firing fraction113 of FIG. 1) from the engine controller 100. Some approaches involvereceiving other types of firing information instead of or in addition tothe firing fraction (e.g., a firing sequence, firing decision, etc.) Theflow regulator may receive a wide variety of other inputs 220 as well,including but not limited to the cam position and the manifold absolutepressure (MAP), which can be used to determine the MAC. Restrictions ofthe exhaust path by the flow regulator may lead to increased cylinderback pressure and decreased fuel efficiency. Accordingly, flow regulatorusage must be a balance between achieving both acceptable NVH and fuelefficiency performance.

Based on these inputs, the flow regulator controller 160 adjusts theflow regulator 202 so that the acoustic effects associated with thereceived firing information are dampened or eliminated. This may beperformed in a wide variety of ways, depending on the needs of aparticular application. In one implementation, for example, one ofmultiple positions for the flow regulator (e.g., positions of the flap212) is set based on the firing information. The flow regulator may beadjusted using any suitable mechanism, such as through the use of astepper motor. Alternatively, a spring load of the flap 212 may bevaried depending on the firing fraction. Although FIGS. 2A and 2Billustrate particular types of flow regulators and exhaust systems, itshould be appreciated that the present invention may be used with a widevariety of devices and structures. In some embodiments, for example, theflow regulator may not involve a flap, but uses a different mechanismfor variably limiting exhaust flow. Various approaches involve a flowregulator that can alternatively severely restrict or entirely allowexhaust flow. In other approaches, the flow regulator has multiplepossible settings that each restrict exhaust flow to a different degree.The flow regulator may also be situated in almost any suitable locationin the exhaust system, such as closer to the engine or in one tailpipeof a dual tailpipe design. More generally, the present invention may bemodified to suit a wide variety of exhaust and engine arrangements,including ones that depart from what is shown in FIG. 2A.

Similar to the use of a flow regulator in the exhaust system, a damper(not shown) may be situated in the engine air induction path to dampennoise generated by the inrush of air into cylinders associated with theopening of the intake valve. The damper may be situated in the airinduction path to absorb or redirect this noise. The damper position mayvary with the firing fraction or it may vary more quickly in response tothe peaks and troughs of the acoustic wave. In some cases the enginethrottle may be used as an acoustic damper and a separate damper is notrequired. When a separate induction damper is used it can take the formof a shutter positioned in front of an air filter; an induction controlvalve or flapper or other suitable form. The appropriate damper positioncan be determined in any desired manner By way of example, look-uptables may provide the desired damper position based on the firingfraction or an indicia indicative thereof (e.g. engine order); or basedon multiple factors (e.g., firing fraction, engine speed, MAC).

Although flow regulator control has been described primarily in thecontext of skip fire operation, it should be appreciated that similarlow frequency acoustic variations can occur during multi-charge levelengine operation and/or multi-level skip fire engine operation andsimilar flow regulation control can be utilized to mitigate the impactof such low frequency acoustic variations.

Referring next to FIG. 3A, an active mount control system 300 accordingto a particular embodiment of the present invention will be described.The active mount control system 300 includes the firing timingdetermination module 120, the firing fraction calculator 112, and theactive mount controller 162. The active mount controller 162 is arrangedto control (e.g., adjust the compliance and/or damping) of the activemounts 302, which physically support the engine 110 or some othervehicle component and couple it to the chassis 304 of a vehicle.Properly configured, the active mounts 302 can help reduce vibration andshaking caused by the engine 110 or some other vehicle component.

The active mount controller 162 receives firing information (e.g., afiring fraction, engine order, firing sequence, indication of a firingdecision, current cylinder number, etc.) from any suitable component,such as the firing timing determination unit 120 and the firing fractioncalculator 112. There are a number of other factors that contribute toengine vibration in addition to the firing decisions and the activemount controller 162 is arranged to receive other inputs 306 indicativeof operating parameters that are relevant to its calculations. Oneparticularly important factor is engine speed (labeled RPM). In variousimplementations, for example, the active mount controller receivesinputs 306 indicating one or more of the mass air charge (MAC), camsettings, manifold absolute pressure (MAP) and/or any other suitableparameters. These parameters are relevant to the calculation of theimpulse that would be expected from any particular firing opportunity.Based on such information, the active mount controller 162 is arrangedto determine an appropriate setting and send appropriate control signalsto the active mounts 302 to adjust the mounts appropriately.

The present invention contemplates a wide variety of control mechanismsthat translate the aforementioned inputs into particular adjustments ofthe active mount. Under particular conditions, for example, as thefiring fraction and/or the engine speed increases, the active mountcontroller sends control signals to stiffen and/or dampen the activemount in order to reduce transmitted motion and vibration. As the firingfraction and/or the engine speed decreases, the active mount may be mademore compliant, so that engine vibration is better absorbed. However,with skip fire engine control, some higher firing fractions may alsointroduce low frequency vibration, depending on the firing sequence thatis used. The active mount controller is arranged to adjust the activemount (e.g., make it more compliant) to address particular firingfractions or sequences that generate such vibration.

The operation and structure of the active mount may vary widely,depending on the needs of a particular application. In some embodiments,for example, the active mount is electrically, hydraulically or vacuumcontrolled. Some active mounts utilize an electroactive polymer or anelectrorheological fluid. In response to certain kinds of anticipatedfiring operations, the active mount controller is arranged toselectively expose the fluid or polymer to an electric field whichmodifies the stiffness and/or damping properties of the mount. Theelectric field is adjusted to control the degree of stiffness and/ordamping properties of the active mount.

In some approaches, it is useful for the active mount controller toinvolve a feed-forward control system, rather than a closed loopfeedback system. A closed loop feedback system for active mountmanagement is used in some prior art vehicle designs. For example, somevehicles use an accelerometer to detect engine vibration, and then usethe feedback from the accelerometer to adjust the active engine mount. Acharacteristic of such feedback-based approaches is that thecorresponding transfer algorithm is more effective for some types ofoperating modes rather than others. Thus, a feedback-based approach canwork well for conventional engine control systems in which theoperational parameters do not rapidly change and engine operation can becharacterized by a few operational modes. In some skip fire engineimplementations, however, the operational characteristics of the enginemay sharply alter from one working cycle to the next, which can make theuse of a feedback-based system less desirable.

The firing information that informs the active mount adjustment mayinclude a firing fraction, an engine order, a firing sequence, firingsequence phase information and/or a discrete fire/no fire decision for aparticular working chamber, etc. Some implementations of the activemount controller are arranged to make adjustments to the active mount ona working cycle by working cycle basis. These implementations require ahigh bandwidth active mount capable of adjustment at frequencies greaterthan of the firing opportunity frequency, often >100 Hz. In otherimplementations the active mount may have a lower bandwidth, i.e. 10 Hzor less, and may be adjusted in response to changes in the firingfraction. More generally, firing information about future firingdecisions is provided to the active mount controller before those firingdecisions are actually implemented in the engine. As a result, theactive mount, rather than being purely reactive, may stiffen and/orbecome more highly damped in anticipation of such decisions, whichimproves the mount's ability to reduce undesirable vibration or motion.

Some designs for the active mount controller involve a finite impulseresponse (FIR) filter. While use of a FIR filter is advantageous becauseits transfer coefficients may be readily determined, other types offilters may be used. A particular example of such an active mountcontroller 162 is illustrated in FIG. 3B. The active mount controller162 includes an FIR filter 350 and an active engine mount adjustmentmodule 352. The FIR filter 350 may receive any of the aforementionedtypes of firing information. In this particular example, the FIR filter350 receives signals in the form of discrete pulses, where a pulserepresents a particular firing event. The magnitude of the pulse maycorrespond to the size of the firing event, as determined by the amountof air and fuel used. The lack of a pulse indicates a skip of a workingcycle for a working chamber, although it should be appreciated that inother implementations the inputs to the FIR filter may take differentforms. The output of the FIR filter 350 is based on the received pulsesand the filter coefficients, which assign a weight to each pulse. Thecoefficients may be fixed at production or be adjustable depending onoperating parameters of the engine. The output of the FIR filter 350 isreceived at the active mount adjustment module 352. The active mountadjustment module 352 then orchestrates changes to the active mountbased on the FIR filter output. It should be appreciated that in variousembodiments the active mount controller 162 receives the pulseinformation prior to the actual firing or skipping of the cylinder, sothat the active mount adjustment module can be adjusted in advance of orcoincident with the actual cylinder firing. Since each working chambercan influence the mounts in different ways, each working chamber mayhave an associated FIR to optimize suppression of NVH originating fromthat working chamber.

Similar to the use of an active engine mount to dampen transmission ofnoise and vibration from an engine to its mounting structure, activemounts may be situated at other locations in the vehicle. As shown inFIG. 3C, one or more active mounts 603 may be situated between an enginesub-frame 607 and vehicle frame members 601. The exemplary system shownin FIG. 3C has four engine sub-frame to frame active mounts 603. Alsoshown in the figure are four active engine mounts 605 between the engine110 and engine sub-frame 607. One or more active mounts may also besituated between the chassis frame and body (not shown in FIG. 3C).

Similarly one or more active mounts may be configured as an activeexhaust hanger to support the exhaust system of a vehicle as shown inFIG. 3D. An exhaust hanger 612 may be permanently bonded to an exhaustpipe 610. The exhaust hanger 612 may be supported by two active mounts612 a and 612 b that attached to the vehicle frame 614. One or more ofthese or similar active exhaust hangers may to used to support theexhaust system along the vehicle undercarriage. For example, three tofive active exhaust hangers may be used, although more or less may beused in some cases. In an analogous manner active mounts may also beused to support a transmission or powertrain and may be incorporatedinto the vehicle shock absorbers (not shown in FIG. 3D). Controllingactive shock absorbers or suspension dampers based on the firinginformation may help to reduce and control low frequency vehicle bodymovement. The stiffness and/or damping of any of these mounts may varywith the firing fraction or some other attribute of skip fire operation.

The described active mount controller 300 is a feed forward control unitthat adjusts the stiffness of the mounts based on the current operatingconditions in order to reduce expected vibrations. When desired,feedback of the resulting vibrations can be used to make the controlleradaptive to further improve the response. To facilitate such feedback,accelerometers can be place at strategic locations on the chassis orvehicle body and their respective signals can also be provided to theactive mount controller 300.

In the discussion above, a few references have been made to engineorder. Engine order is a normalized frequency where the normalization isrelative to the frequency corresponding to one revolution of the enginecrankshaft. Thus, for example, a conventional four stroke, four cylinderpiston engine operating in a normal (non-skip fire) mode would have afiring frequency that occurred at the second engine order (2E) becausetwo cylinders fire each crankshaft rotation. Thus the firing frequencywould be twice the engine crankshaft rotation frequency (E). Similarly,a six cylinder engine would have a firing frequency having an order ofthree (3E), while an eight cylinder engine would have a firing frequencyhaving an order of four (4E). With skip fire operation, fractionalorders are often utilized. For example, a four-stroke, eight cylinderengine operating at a firing fraction of ⅓ would have a firing frequencyorder of four thirds ( 4/3E) meaning that on average, 1⅓ cylinders arefired every rotation of the crankshaft. It should be appreciated thatwhatever the firing frequency order harmonics and possibly sub-harmonicsof this order will also be generated. Generally these associatedharmonic frequencies need to be considered, and in some cases mitigated,to obtain acceptable vehicle NVH performance.

Many skip fire controller are constrained to allow a defined set ofavailable firing fractions, patterns or sequences. By way of example,the Applicant has implemented a skip fire controller having 29 availablefiring fractions that may be used when conditions permit, with theirassociated firing sequences being constrained to fire in a most evenlyspaced manner whenever possible. The available fractions include anyfractional value between zero and 1 having a denominator or 9 orless—e.g., 0, 1/9, ⅛, 1/7, ⅙, ⅕, 2/9, ¼, 2/7, ⅓, ⅜, ⅖, 3/7, 4/9, ½, 5/9,4/7, ⅗, ⅝, ⅔, 5/7, ¾, 7/9, ⅘, ⅚, 6/7, ⅞, 8/9 and 1. Each of these firingfractions has an associated firing fraction engine order and thus thecontroller has a defined set of operational orders. More generally, mostany skip fire controller with a defined set of available firing patternswill typically have a corresponding defined set of available firingfraction orders. Thus, the current firing fraction operating order canreadily be reported to, or determined by the active noise cancellationcontroller 164, the active mount controller 162 or other suitablecontroller. It should be appreciated that in the exemplary controller,the engine order associated with many of the possible firing fractionswill be a fractional order. For example, an 8-cylinder engine operatingat a firing fraction of 2/7 would have an order of 8/7E.

The engine order associated with any given operational firing fractionis a construct that is useful in designing filters suitable for use inNVH management. This is because the firing frequency will be the ordertimes the engine speed and firing frequency is central to skip fireinduced NVH issues. By way of example, the filter coefficients that areappropriate for operation at a particular firing fraction may be basedupon the order and the engine speed (RPM) with the appropriate filtercoefficients being stored in a look-up table (LUT) having twoindices—order and engine speed. If a digital filter is used with avariable clock based on engine speed, the appropriate filtercoefficients can be stored in a one dimensional look-up table based onengine order. Since the engine order is based on the firing fraction,the firing fraction or any other parameter indicative of firing fractioncan be used as the index as well.

In many applications, the settings of the active engine mounts may bebased primarily on the firing fraction (engine order) and the enginespeed. In such a system, the appropriate mount settings for anyparticular skip fire operating condition can readily be retrieved from alookup table based on those two parameters. In other embodiments,additional operating conditions such as mass air charge (MAC), orsettings indicative thereof can be used as another dimension for suchtables. Of course, in other embodiments, the appropriate settings can bedetermined algorithmically or using data structures other than lookuptables.

Although the feed forward active engine mount control described abovehas been described primarily in the context of skip fire operation, itshould be appreciated that similar types of vibration can occur duringmulti-charge level engine operation and/or multi-level skip fire engineoperation and that similar control of active engine mounts can beutilized to mitigate the impact of such cylinder output level modulationinduced vibrations.

Referring next to FIG. 4A, an active noise cancellation system 400according to a particular embodiment of the present invention will bedescribed. The active noise cancellation system 400 includes the firingtiming determination unit 120, the firing fraction calculator 112 andthe active noise cancellation controller 164. The active noisecancellation controller 164 is connected with one or more speakers 402situated in a vehicle. The speakers 402 may be situated in any locationin the vehicle where noise cancellation is desired, including but notlimited to a location near the driver seat, front passenger seat, rearpassenger seats, engine air intake 406 and/or the exhaust tailpipe 404.In addition speakers may be placed at various locations in the passengercabin. Often the noise cancellation system 400 will simply use the audiosystem cabin speakers that would otherwise be present in the vehicle.

The active noise cancellation controller 164 is arranged to control thespeakers so that they emit sounds that cancel out undesirable acousticeffects generated by the engine. The wavelength, amplitude, frequencyand other characteristics of the canceling sounds are based on firinginformation received by the active noise cancellation controller 164. Aspreviously discussed, the firing information may involve any suitableinformation related to future operation of the working chambers of theengine. In the illustrated embodiment, for example, the firing fractioncalculator 112 sends firing fraction and/or engine order information tothe active noise cancellation controller 164 while the firing timingdetermining unit 120 sends firing sequence/decision and/or phaseinformation to the active noise cancellation controller. The exactparameters of the cancelling sound waves may be determined using anysuitable mechanism, such as a lookup table. The active noisecancellation controller 164 then orchestrates the emission of thecanceling sounds from the speakers 402. As a result, the emittedcanceling sounds at least partially cancel the noise generated by thoseengine operations that were characterized by the aforementioned firinginformation.

The noise generated by the firing or operation of a particular workingchamber may be affected by engine speed and distinctive characteristicsof a particular working chamber (e.g., its relative position in theengine or vehicle) and its firing history. Some implementations takethis into account in determining a suitable noise cancelling sound. Inthe illustrated embodiment, for example, the active noise cancellationcontroller 164 receives a firing decision with respect to a particularworking chamber as well as information indicating the identity or numberof the working chamber (cylinder data 406), as well as firing historydata 408 on the working chamber. The firing history data may take avariety of forms. For example, the firing history data may indicate anumber of skips or fires over a predetermined number of consecutiveworking cycles. The active noise cancellation controller 164 thendetermines a noise cancelling sound based on the above information.

Referring next to FIG. 4B, a flow diagram describing methods forgenerating noise cancelling sounds according to a particular embodimentof the present invention will be described. More specifically, the flowdiagram compares a prior art method against a particular implementationof the present invention. Prior art sound cancellation apparatus 401describes a prior art approach. In this approach, undesirable noise isgenerated by a particular sound source 409, such as the engine. Thesound is heard in a cabin of a vehicle and detected by a microphone 407.A signal generated in the microphone 407 is directed to the noisecancellation controller 410. The noise cancellation controller 410directs a signal to speaker 414 that seeks to cancel the noise generatedby the sound source in certain regions, particularly occupied regions ofthe vehicle cabin. This process, however, involves various delays, shownschematically in block 408. The delays arise from the transit time ofthe sound from the source to the microphone, the transmission of thesignal from the microphone to the noise cancellation controller,processing in the noise cancellation controller and lag in the speakerresponse to signal input from the noise cancellation controller.

Noise cancellation apparatus 411 describes a particular implementationof the present invention. In this approach, firing information isgenerated in an engine controller 100. This information is inputted bothto the sound source 409 (typically the engine) and into a suitable model416 that may be incorporated as part of an active noise cancellationcontroller 417. The active noise cancellation controller 417 generates asignal that is directed to speaker 414. The firing information allowsthe active noise cancellation controller 417 to potentially determine asuitable noise cancelling sound before the sound reaches the cabin orregion of interest. As a result, delay 408 is mitigated and the noisemay be canceled before it is heard by occupants of the vehicle. In somecases the speaker 414 may emit the noise cancellation soundsubstantially synchronized with the firing impulse from the internalcombustion engine. The relative timing of the noise cancellation soundto the firing impulse may be adjusted so that the sound from the firingimpulse and noise cancellation sound arrive substantially simultaneouslyat the ears of the vehicle occupants. The variable delay block 163(FIG. 1) is one method to provide the appropriate delay to synchronizethe noise mitigation with the engine operation.

The active noise cancellation controller 164 may determine a suitablenoise cancelling sound in a wide variety of ways, depending on the needsof a particular application. FIG. 4C illustrates one suchimplementation. In FIG. 4C, the active noise cancellation (ANC)controller 164 includes a finite impulse response (FIR) filter 450 andan ANC correction module 452. Firing decisions may be represented in theform of pulses or a pulse wave. In various implementations, a pulsesignal represents a firing event, while an absence of a pulse signalindicates a skip of a working chamber. The signals are then used as aninput to the FIR filter 450. The output is then sent to the ANCcorrection module 452. The ANC correction module 452 determines asuitable noise cancelling sound based on the received filter output. TheFIR filter coefficient values may be fixed or adaptive. Fixed values maybe chosen based on acoustic modeling or calibration data. Adaptivevalues may be chosen using appropriate cost function(s) to minimize thenoise. Least Mean Squares (LMS) and Recursive Least Squares (RLS) aresuitable algorithms for filter adaptation, although other optimizationalgorithms can also be used. It should be appreciated that the aboveexample describes only one possible implementation of the active noisecancellation module with an FIR filter, and that various modifications,such as an additional filters, a different input set or calculationmethodology, one FIR filter per working chamber are also possible.

Skip fire and other cylinder output level modulation operation tends tohave multiple periodic components that can contribute to undesirablesounds and the phase of such periodic components is important for activenoise and/or vibration control. To illustrate the issue, consider afiring sequence that would occur when a firing fraction of ⅖ (40%) isused with a constraint of most even possible spacing of the firings. Inthat circumstance the resultant firing pattern would be: FssFs. That is,one fire (F) is followed by two skips (s), and the following fire (F) isfollowed by a single skip (s), before the pattern is repeated. Thus, theFssFs pattern that repeats over the course of five firing opportunitiesis one recurring pattern that has associated acoustic and vibratorycharacteristics. In addition, the specific cylinders that are beingfired at any time will have their own associated effects which are alsoperiodic in nature. For example, consider an 8 cylinder engine having afiring order of cylinders 1-8-7-2-6-5-4-3. When operated at thedescribed 40% firing fraction, the engine has a specific cylinder firingsequence that repeats itself every five engine cycles as illustratedbelow. This recurring pattern also has associated acoustic and vibratorycharacteristics.

18726543 18726543 18726543 18726543 18726543 FssFsFss FsFssFsF ssFsFssFsFssFsFs sFsFssFs

In practice any particular repeating firing fraction or sequence mayhave multiple frequencies of concern. To accommodate this, the activenoise cancellation (ANC) controller 164 may include a set of filters 450(e.g., multiple FIR filters), with each filter being configurable toaddress a particular frequency (or engine order) of concern in thecurrent operational state. The filters may be arranged in parallel, sothat any output is always available and from this set the particularoutput used is based on the firing fraction or frequencies of concern.This ability to target frequencies/orders of concern at the same time isa particularly powerful tool in reducing noise (and vibrations) duringskip fire operation. In theory, any number of filters 450 can beprovided to handle different frequencies of concern. However, ingeneral, a limited number of frequencies are of concern. For vibrationsgenerally the fundamental or perhaps the second and/or third orderfrequencies need to considered, since human body perception is greatestat low frequencies (1-10 Hz). Human tactile vibration perception isimportant for the steering wheel and here frequencies in the 1-250 Hzrange should be considered. Human acoustic perception extends to higherfrequencies and frequencies >250 Hz should be considered for acousticnoise mitigation. Human sound perception, psychoacoustic, is oftencomplex and whether a sound is pleasing or unpleasant often needs to bedetermined empirically. Obviously the transfer paths between the NVHsources and the vehicle occupants also needs to be considered indetermining the potential impact of various frequencies. Regardless thefrequency(ies) of concern for any particular firing fraction/engineorder and engine speed combination, the appropriate filter coefficientscan readily be determined experimentally. Of course, if a sufficientlyaccurate acoustic model is available, the appropriate filtercoefficients could be determined by mathematical modeling.

When actively controlling sound or vibration characteristics associatedwith skip fire operation of an engine, it can also be important to knowthe pattern phase of any firing pattern that may be in use. That is, thelocation within a repeating pattern in relation to repeating enginecycles. Such pattern phase information can be provided by the firingtiming determining module 120 or any other suitable source. Additionallyinformation regarding spark and intake/exhaust valve timing may be usedto accurately synchronize the sound modifying device with the engine.Information regarding cylinder mass air charge (MAC) may additionally beused to determine the proper magnitude for the sound produced by thesound modifying device. Larger MAC values are generally associated withlouder engine produced noise and thus the magnitude of the soundproduced by the sound modifying device must also be increased toeffectively cancel the engine noise. Information on the MAC and timingcan be provided by the signal line 161 or any other suitable source.

Many sound cancellation systems utilize multiple speakers (e.g., theexisting cabin speakers). Since sound takes some time to travel from itssource, it may be desirable to adjust the response of the speakers on aspeaker by speaker basis to ensure that the desired cancelling occurs atthe appropriate locations within the cabin (e.g., where the vehicleoccupants would sit). To facilitate individual adjustment of the speakerresponse, different filters or filter sets may be used for each speaker.Still further, the sound characteristics associated with a particularfiring may be different on a cylinder bank or a per cylinder basis. Assuch, in some implementations it can be advantageous to providedifferent filters (or filter sets) for use in conjunction with differentcylinder firings on an individual or per bank basis. It should beappreciated that the actual number of independently configurable filtersthat are appropriate for any given system will depend in significantpart on the acoustic characteristic of the engine/induction/exhaustsystem in use and the level and sophistication of noise cancellationdesired.

Filter updates are slow compared to frequencies being filtered. Enginespeed can change by 1000 rpm per second. This rapid change is similar tofrequencies the ANC system is trying to eliminate. Classic filteradjustment methods will fail if applied to ANC. One solution to thisproblem is to provide a bank of parallel filters and smoothly switchbetween them as the engine operating parameters, such as firing fractionand engine speed, vary. Alternatively a more directed method ofadjusting the filter coefficients, using the advanced knowledge of thefiring fraction, may be employed.

One example of a bank based difference is an 8 cylinder engine havingtwo banks of four cylinders with an asymmetric Y-pipe connecting theexhaust manifolds from the banks. The length of the exhaust paths maydiffer between firings in the two different banks due to the differentY-pipe segment length and it may be desirable for the active noisecancellation (ANC) controller 164 to account for these differences whendetermining the appropriate noise cancelling signal(s). More broadly,different exhaust manifolds/exhaust systems often have differ exhaustpath lengths on a cylinder by cylinder basis and in some instances,those differences may be significant enough for the active noisecancellation controller to differentiate the noise cancellation responsebased on the specific individual cylinder(s) being fired.

It should be appreciated that it is easier to cancel out lower frequencysounds. By way of example, it is typically practical to substantiallycancel out sounds at frequencies below about 100 Hz using conventionallymounted speakers within the cabin. It is possible with judicious speakerplacement and phase adjustment between the cabin speakers to extend thecancelling range to about 600 Hz. In this case the sounds are generallyonly cancelled in the location of the heads of the vehicle occupants.Sounds above that range are generally difficult to cancel in manyautomotive cabins. Of course these ranges are only given by way ofexample and the applicable ranges will vary significantly based onfactors such as cabin geometry, speaker placement, the region(s) wherehigh levels of cancellation are desired, etc.

In some embodiments, a speaker 402 is placed near or at the tailpipe404, which is the combustion gases exhaust orifice. The tailpipe tendsto be one of the largest sources of engine noise. Such co-location ofthe speaker with the source of the noise makes it easier to cancel thenoise and expands the frequency range over which noise cancellation canbe successfully employed. Another significant source of sound is theintake manifold and co-location of a speaker 402 near the intakemanifold can be particularly useful for cancelling or otherwise managingintake related sounds.

It is believed that conventional automotive sound cancellationtechniques use a feedback based approach to cancel out noise through thespeakers. That is, the sound level is sensed and appropriate correctivefeedback is applied to the speakers to cancel out the undesired sounds.In contrast, the approach described above is a feed-forward approachbased on knowledge of what the engine is expected to be doing. In theprimary described embodiment, knowledge of the skip fire firing sequenceis used to help cancel out noises that would otherwise be generated bythe engine/exhaust system/etc. However, it should be appreciated thatthe same feed forward approach can be applied to mitigate otheranticipated sounds is a proactive, prospective manner By way of example,other sounds that are well suited for feed forward control include airintake related sounds (which are heavily based on throttle position andengine speed), intake/exhaust valve noise and transmission noise.

The described feed-forward approach can also be combined with moretraditional feedback based control to make the system adaptive andfurther mitigate or manage cabin noise. In such cases microphone 407detects cabin noise which is used as an additional input by the noisecancellation controller 410. It is often useful to place the microphone407 close to the speakers 414 to achieve a high cancellation frequency.This type of system can be used to cancel road noise, which is difficultto predict in advance.

The vibration management approach described above with reference to FIG.3A contemplates adjusting the stiffness/damping of active engine mountsin an effort to dampen firing pattern induced engine vibrations in anintelligent manner. In still other embodiments, active vibration control(AVC) can be accomplished in a manner that is quite analogous to activenoise cancellation (ANC) by effectively adding vibration to the chassisor engine. The induced vibrations can be selected in an effort to cancelout expected vibrations (e.g., to offset or cancel out skip fire inducedvibrations in the vehicle), and/or to provide a desired vibrationprofile (e.g., to mimic the feel expected during all cylinder operationor some other vibration profile deemed desirable in a particularapplication). An exemplary active vibration control embodiment 600 isdescribed with respect to FIG. 6. In this embodiment an active vibrationcontroller 167 is arranged to direct the operation of one or more voicecoil motors or other type of electromagnetic actuator(s) or shaker(s)620 mounted at appropriate locations on a vehicle chassis/frame 304. Thespecific placement of the voice coil motors will vary based on thenature and location of the vibrations sought to be damped. By way ofexample, in the illustrated embodiment the voice coil motors areintegrated with the engine mounts and support the engine 110.

Additionally in some embodiments voice coil motors may be attached to afloor plan, or steering wheel column, and/or occupant seat. The activevibration controller 167 actuates the voice coil motors 620 atappropriate times to induce the desired vibration related effects on thevehicle.

The active vibration controller 167 receives firing fraction, firingsequence and/or engine order information from the firing fractioncalculator 112, specific firing timing and/or sequence phase informationfrom firing timing determination module 120 and the current engine speedfrom the ECU or other available source. Based on such firing relatedinformation and any additional desired inputs, the active vibrationcontroller determines what vibratory inputs are desired and then directsor actuates the vibration actuators (e.g., voice coil motors 620) in thedesired manner Although the described voice coil motors work well as thevibration actuators, it should be appreciate that a variety of othervibratory mechanisms can be used in place of the described voice coilmotors when desired. In general, voice coil motors can be usedeffectively to induce vibrations at frequencies up to approximately 500Hz, which adequately covers the range of vibrations that tend to be ofmost concern.

The architecture of the active vibration control system may besubstantially the same as any of the active noise cancellationarchitectures previously described, although rather than drivingspeakers to induce sound cancelling signals, actuators (such as voicecoil motors) are driven to induce vibration canceling signals in theengine mounts (or elsewhere). In place of any microphone used to detectacoustic signals, accelerometers or other vibration sensors can be usedto detect actual vibrations in a feedback loop. The result is a feedforward system that uses skip fire firing information to reduceperceptible vibrations in a vehicle. Of course, other architectures canbe used as well. When desired, feedback of the actual vibrations can beused to make the system adaptive and further refine the control. Asdiscussed above, skip fire operation can induce a number of differentperiodic patterns which can potentially induce vibrations at differentfrequencies (and having different associated orders) and these differentfrequencies/orders can readily be identified and addressed at the sametime using the described approach.

In most circumstances, the desired feel will be little or no perceptibleengine induced vibrations. The described active vibration control can beused to help mitigate vibrations by inducing vibrations that at leastpartially cancel out vibrations that are expected to be induced by skipfire operation of the engine. However, in some circumstance it may bedesirable to provide a particular feel. In such circumstances, thedescribed active vibration control can be used to help define(synthesize) the overall vibration effect by controlling the vibrationsassociated with each cylinder firing opportunity on a firing opportunityby firing opportunity basis. The net result of this approach is adesired feel. For example, the vibration actuators can be utilized tomimic the feel of a fired cylinder during each skip so that the overallfeel of the vehicle mimics the feel that would occur under all cylinderoperation at any desired throttle level. Thus for example, the vehiclevibration could be controlled to be substantially the same regardless ofwhether the engine is operating in a skip fire mode or an all cylinderfiring mode. Sound can be actively managed in much the same way asvibrations. Thus, another active sound management approach contemplatescontrolling the sounds associated with each cylinder firing opportunityon an individual basis such that the net result is the generation of adesired sound. This can be used to give a skip fire controlled vehiclethe powerful “growl” often associated with V8 engine operation.

Such sound and vibration control can be provided throughout skip fire orother cylinder firing level modulation operation or only at designatedtimes. For example, sound/vibration control may be desirable in responseto certain detected conditions (e.g., accelerator pedal stomp orsignificant increases in pedal position, etc.) or only during operationin skip fire conditions that are more susceptible to generatingundesirable conditions (e.g., vibrations tend to be more noticeableduring skip fire operation at lower engine speeds and/or when usingcertain firing fractions/patterns that are inherently rougher so activevibration control may be more desirable when operating in thoseconditions). Using the pedal stomp example, some studies have suggestedthat drivers tend to associate sounds and vibrations in the 300 Hz range(e.g. 150 to 350 Hz) with a feeling of power, so sounds/vibrations inthat range could be emphasized when pedal stomp is detected. Thus, itshould be appreciated that in various embodiments, the sound and/orvibrations control system can readily be designed for noise/vibrationcancellation, to synthesize a desired feel, or to provide a more steadystate feel over varied operation.

As previously mentioned, the sounds associated with a skipped firingopportunity will be quite different than the sounds associated with afired working cycle. These discrepancies can result in undesirableaudible beats. Theoretically, such beats can be eliminated and a desiredsound can be achieved by simply (a) canceling a small portion of thenoise generated by each cylinder firing or introducing an appropriateinterfering signal so that resultant sounds during the firing matchesthe desired sound; and (b) generating the appropriate incremental soundsduring skipped working cycles. If both are done, the net resulting soundwill match the desired sound.

Another active sound management architecture that is particularly wellsuited for managing engine exhaust related sounds in skip firecontrolled engines will be described with respect to FIG. 7. In theillustrated embodiment active sound management system 700 is acalibrated feed forward system that utilizes a pair of adjustable FIRfilters 704, 706 to drive a speaker 710 in a manner that help shapes thevehicle sound. Depending on whether a working cycle is a skip or a fire,the engine will generate a different noise. Each time a working cycle isskipped, a pulse is sent through filter 704 which causes the speaker 710to generate a pulse filling sound. Each time a working cycle is fired, apulse is sent through filter 706 which causes the speaker 710 togenerate a sound modify the resultant firing sound in the vehicle cabin.Depending on the goals of the system, the pulse modification can bearranged to substantially cancel sounds associated with the firing,partially cancel (mitigate) the resultant sound associated with thefiring, or simply modify the nature of the resulting sound. In somecases, filter 706 may block any signal to the speaker 710 so that theoriginal engine noise is unmodified during a fire. In this case the FIRfilter 704, which is active during a skip, may be configured to generatea sound substantially imitating the sound of an engine fire. This willproduce a smoother output sound, which may be pleasing to the vehicleoccupants. Regardless of the goals of the system, the filter used tocontrol the sound generated by the speaker 710 changes based on whethera particular working cycle is skipped or fired. A driver 712 receivesthe skip/fire decisions from the firing timing determination module 120and sends that appropriate pulse to filter 704 or 706 based on theskip/fire decision. The timing of the pulse is governed by timergenerator 715. In general the timing of sound associated with an exhaustpulse is base primarily upon the timing of the exhaust valve opening.Thus, the timer generator may receive an input indicative of the camangle and cam phaser setting to determine the timing of the valveopenings. This timing information is sent to driver 712 which determinesthe appropriate time to send the pulses to the appropriate filters704/706 based on the valve opening timing and any other relevantfactors.

For engines operating with cylinder output level modulation, theconcepts described above may be extended. For example, an engine capableof three distinct levels, zero, a low torque output, or a high torqueoutput, will make three distinct sounds at each firing opportunitydepending on the cylinder level. In this case, three different filtersmay be used, one for each level. An operational cylinder output levelmodulation mode may be characterized by a firing fraction and a levelfraction. The firing fraction gives the fraction of fires to firingopportunities and the level fraction gives the fraction of high levelfires to total fires.

The coefficients used in the filter are set by filter coefficient setter720. The filter coefficient setter 720 selects the appropriate filtercoefficient base on current operating conditions. These may vary basedon one or more operating parameters such as engine speed. Whenappropriate, the coefficients can vary as a function of multipleparameters such as engine speed and air charge, etc. Thus, the filtercoefficient setter 720 receives indication of the engine operatingparameters needed to select or calculate the appropriate coefficients.As previously mentioned, look-up tables work well for this purposealthough other data structures, can be used and/or appropriate valuescan be determined algorithmically if desired. When lookup tables areused, the received engine operating parameters may be used as indicesfor the lookup tables.

As discussed above, the sounds associated with any particular firing mayvary based on the particular cylinder being fired or the bank that thecylinder resides in. Therefore, when desired, one or both the filters704 and 706 can be implemented as a set of filters, with each filterbeing associated with a particular bank or cylinder. Of course, the setof filters is generally more useful in filter 706 which is associatedwith cylinder firings. Alternatively, if the filter is responsiveenough, the filter coefficients can be changed on a working cycle byworking cycle basis to accomplish the same effect.

The active sound management system of FIG. 7A can be made adaptive byreplacing filter coefficient setter 720 with an adaptive unit 740 thatalso receives feedback from a microphone 745 as illustrated in FIG. 7B.

To train the system, the adaptive unit 740 may be arranged to measureactual vehicle sounds in an isolated environment that is free from othertypes of sounds. The engine can be operated over its entire operatingspeed and load range. The vehicle may also be operated at alltransmission gear ratios. Under each operating condition the frequency,magnitude and phase are measured at each point of interest, such as theanticipated location of the driver's ears. The adaptive unit may thenforward this control data into a filter coefficient setter 720. Thefilter coefficient setter 720 in turn defines the appropriate set offilter coefficients which determine the magnitude and phase for eachfrequency component to achieve the desired sound modification at thepoint of interest. With this arrangement, the filter coefficients thatare appropriate to deliver the desired sound are determinedexperimentally. This is often more accurate than an analytical approachto determine the coefficients because of the complex nature of thevarious transfer paths.

Although FIGS. 7A and 7B show sound management systems, it should beappreciated that substantially the same architecture can be used foractive vibration control as well with the speaker simply being replacedby appropriate actuators.

In the descriptions above, both feedback and feed forward approaches toNVH management have been described. In feedback based approaches, noisesand/or vibrations are detected and then measures are taken to at leastpartially cancel out or mitigate the detected item and/or to manage theresultant auditory or vibratory response. Feedback based systems canwork well because electronic sensors and the described controllers canoften detect undesirable sounds and vibrations and take appropriatecorrective actions before they are perceived by vehicle passengers. Theyalso have the advantageous characteristic that they can account foreffects that cannot be effectively modeled. In feed forward systems, thesystem's knowledge of the expected firing sequence can be used toproactively mitigate or manage the auditory and vibratory responseconcurrently with the firing events that would otherwise generate anundesirable response, which can mitigate or manage auditory andvibratory effects at the time they would otherwise occur. Thus, when anexpected response can be effectively modeled, as is often the case withskip fire control, feed forward approaches can provide better control.In many circumstances, it may be desirable to combine both feedback andfeed forward control to manage NVH effects.

Referring next to FIG. 5A, an active torsional vibration damper controlsystem 500 according to yet another embodiment will be described. Thetorsional damping control system includes the engine controller 100 andthe torsional vibration damper controller 166. The engine controller 100provides firing information (e.g., a firing fraction, engine order,etc.) to the vibration damper controller 166. Based on the firinginformation, the vibration damper controller 166 determines a dampinglevel that is appropriate for the commanded skip fire operatingconditions and communicates with and controls a torsional vibrationdamper 502 to provide the desired damping. Given the nature of torsionaldamping, firing fraction or engine order or a related parameter isgenerally the most useful firing information for setting the desireddamping level. However, when desired, the firing sequence, firingsequence phase and/or a firing decision for one or more working chamberscan be utilized as well.

As shown in FIG. 5B the vibration damper 502 may be situated on thedrive line 506, between the transmission 504 and the drive wheels 508 ofa vehicle 510. The vibration damper 502 provides a non-rigid couplingbetween the transmission 504 and drive wheels 508. The vibration dampermay incorporate an electrorheological fluid or a magnetorheologicalfluid to provide a non-rigid mechanical coupling. The mechanicalproperties of these fluids may be altered by applying an electrical ormagnetic field, respectively. Thus, the stiffness of the mechanicalcoupling between the transmission and drive wheels may be changed byaltering the mechanical properties of these fluids. The fluid propertiesmay be controlled to avoid or dampen torsional and bending resonancesthat may arise in the driveline from skip fire operation providingactive torsional control. Alternatively, the vibration damper 502 mayincorporate a mechanical clutch or mechanical system to vary thestiffness and/or damping of the coupling between the transmission 504and the drive wheels 508. These types of torsional vibration damperstend to be fairly good at damping lower frequency oscillations.

Referring next to FIG. 8, yet another embodiment will be described. Inthis embodiment, a variable spring absorber 805 is incorporated into thepowertrain between the engine 110 and the transmission 809. By way ofexample, suitable variable spring absorbers have been developed byBorgWarner. Variable spring absorbers are sometimes referred to asvariable spring rate absorbers or simply variable absorbers. In general,a variable spring absorber is configured to efficiently transmit torquebetween drive train components, but to significantly dampen torsionalvibrations at a designated frequency. The designated damping frequency(spring rate) may be programmatically adjusted during driving to tunethe frequency of the vibrations that are being dampened at any giventime. In the embodiment of FIG. 8, the noise/vibration reduction unit102 includes an absorber controller 169 that controls the spring rate ofthe variable spring absorber. More specifically, the absorber controller169 is configured to set and adjust the designated damping (absorption)frequency of the variable spring absorber during driving.

The absorption frequency (spring rate) of the variable spring absorbermay be set based on a skip fire or other cylinder output levelmodulation characteristic. Often, the most significant vibrations inskip fire/cylinder output level modulated engines are related to thefrequency at which a firing sequence repeats. Stated another way, theyare a function of the minimum repeating pattern length (MRPL) and enginespeed. In the context of skip fire operation with most evenly spacedfirings, the minimum repeating pattern length will be the denominator ofthe (irreducible) firing fraction. That is a firing fraction with nocommon integer factor between the numerator and denominator. In someembodiments, the absorber controller 169 sets the absorption frequencyof the variable spring absorber 805 to the frequency that the firingsequence repeats at the current operational conditions. For afour-stroke engine, that frequency can be determined by the formula:F _(abs)=[(RPM/60)*(Cylinder Count/2)]÷MRPLWhere F_(abs) is the absorption frequency, the Cylinder Count is thenumber of engine cylinders and MRPL is the minimum repeating patternlength.

In the context of skip fire engine operation, the minimum repeatingpattern length (MRPL) is the denominator of the irreducible operationalfiring fraction. Therefore, it should be appreciated that in the contextof skip fire engine operation, for any given engine speed, theabsorption frequency F_(abs) would be the same for all firing fractionshaving the same denominator. That is, the absorption frequency would bethe same for firing fractions of ⅓ and ⅔; it would be the same forfiring fractions of ⅕, ⅖, ⅗, ⅘; it would be the same for all firingfractions having a denominator of 7; etc.

In the context of multi-charge level engine operation (in which allcylinders are fired, but different cylinders may be fired at one of twodifferent levels), the minimum repeating pattern length is determined bya ratio of high and low output firing. As previously described thisratio may be expressed as a level fraction, which is the ratio of hightorque output fires to total fires. Assuming that the high and lowfiring are most equally spaced, the minimum repeating pattern length isthe irreducible denominator of the level fraction. In the context ofmulti-level skip fire (in which fired cylinders may be skipped or firedat one of two levels), the minimum repeating pattern length is generallybased on both the firing fraction and level fraction. The minimumrepeating pattern length has a different dependence on the levelfraction than on the firing fraction.

FIG. 9 shows a table 900 that illustrates some examples of differentfiring fraction and level fraction combinations. In table 900 the firingfraction numerator FF_(num), the firing fraction denominator FF_(den),the level fraction number LF_(num), and the level fraction denominatorLF_(den) are listed in separate columns. In column 910 the greatestcommon factor of the firing fraction numerator and level fractiondenominator (gcf(FF_(num), LF_(den))) are calculated and tabulated. Theminimum repeating pattern length (MRPL) is given by the product of thefiring fraction denominator (FF_(den)) and the level fractiondenominator (LF_(den)) divided by the term in column 910.

As an example, consider row 920 of table 900. In this case the firingfraction is ½ and the level fraction is ⅔. The values are FF_(num)=1,FF_(den), =2, LF_(num)=2, and LF_(den)=3. The greatest common factor ofFF_(num) and LF_(den) is 1. Thus, the MRPL can be determined as 2*3/1=6.A firing pattern associated with this combination is HsHsLs,HsHsLs whereH represents a high output fire, L represents a low output fire, and srepresents a skip. The repeating patterns are separated by a common.Inspection of the pattern shows that the pattern repeats every 6 firingopportunities, consistent with the result in table 900.

Consider now a different case, the firing fraction and level fractioncombination shown in row 930. Here the firing fraction is ⅓ and thelevel fraction is ½, so the firing fraction and level fraction valuesare switched from the previous example. The values are FF_(num)=2,FF_(den)=3, LF_(num)=1, and LF_(den)=2. The greatest common factor ofFF_(num) and LF_(den) is 2. Thus, the MRPL can be determined as 3*2/2=3.A firing pattern associated with this combination is HLs,HLs, where acomma separates the repeating pattern. Inspection of the pattern showsthat the pattern repeats every 3 firing opportunities, consistent withthe result in table 900. Comparing this example with the previousexample demonstrates the asymmetric nature of the firing fraction andlevel fraction in determination of the minimum repeating pattern length.

The other examples in table 900 show various other cases of firingfraction and level fraction combinations. In some cases, the MRPL isunaffected by switching the values of the FF and LF and in other casesswitching the FF and LF values results in a change in the MRPL.

The absorber controller 169 is configured to adjust (tune) theabsorption frequency in a feed forward manner based on changes in theoperational engine speed and the MRPL. In embodiments that utilizedynamic skip fire or other dynamic cylinder output level modulation, theeffective firing fraction and MRPL may change relatively often duringmany normal types of engine operation. For example, firing fractionchanges often occur as frequently as every few seconds or less when arelatively large number of firing fractions are available/supported.Similarly, the engine speed can change relatively rapidly during manytypes of engine operation. Therefore, the absorber controller 169 mayupdate the absorption frequency relatively rapidly. For example, theabsorption frequency may be updated on the order of once a second. Itshould be appreciated that if the firing fraction is changing veryrapidly, for example, during rapid acceleration where the firingfraction may change several times a second, it is not necessary for theabsorption frequency to change as rapidly since there is no repeatingpattern and thus no time for vibrations to build up in the powertrain.

The desired absorption frequency can be determined in a wide variety ofdifferent manners, including calculating the absorption frequencyalgorithmically based on current operating parameters, through the useof lookup tables that utilize factors such as engine speed and one of(i) firing fraction, (ii) minimum repeating pattern length, (iii) engineorder, (iv) a harmonic of any of the foregoing, etc. as indices for thelookup table, or through the use of other suitable data structures.

The figures refer to subcomponents and functional blocks that performvarious functions. It should be appreciated that some of thesesubcomponents may be combined into a larger single component, or that afeature of one subcomponent may be transferred to another subcomponent.The present invention contemplates a wide variety of control methods andmechanisms for performing the operations described herein, and is notlimited to what is expressly shown in the figures. For example, in thevarious illustrated embodiments, the firing information provided to thevarious vibration and noise management controllers is typicallydescribed as coming from the firing fraction calculator 112 and/or thefiring timing determination module 120. Although this architecture workswell, it should be appreciated that such information can come from anysuitable source. For example, in many implementations, the functionalityof the firing fraction calculator and firing timing determination modulewill be accomplished by an engine control unit (ECU) or a powertraincontroller that may not incorporate readily identifiable modules thatperform the corresponding functions. In still other embodiments, thedesired skip fire firing sequences may be determined in very differentmanners. Regardless of how the firing sequences are determined, therelevant firing related information can readily be provided to thevarious noise and vibration related controllers. In the illustratedembodiments, the controllers are typically shown as independent units tofacilitate the ease of explanation. However, again, the functionality ofsuch units can readily be incorporated into an ECU or powertraincontroller or any other suitable control unit. Indeed, it is anticipatedthat in most commercial applications, the functionality of the variousdescribed vibrations controllers would be incorporated into the ECU orpowertrain controller as opposed to being embodied as discretecomponents.

The described embodiments work well with skip fire engine operation. Ingeneral, skip fire engine control contemplates selectively skipping thefiring of certain cylinders during selected firing opportunities. Thus,for example, a particular cylinder may be fired during one firingopportunity and then may be skipped during the next firing opportunityand then selectively skipped or fired during the next. This iscontrasted with conventional variable displacement engine operation inwhich a fixed set of the cylinders are deactivated during certainlow-load operating conditions. In dynamic skip fire control, firingdecisions may be made on a firing opportunity by firing opportunitybasis. In some implementations, working chambers are fired under optimalor close to optimal conditions, that is the conditions that yieldmaximum fuel efficiency. In some embodiments, during the firing ofworking chambers the throttle is positioned to maintain a manifoldabsolute pressure greater than 70, 80, 90 or 95 kPa to minimize pumpinglosses. Rather than using primarily MAP control to match the engineload, a skip fire controlled engine primarily varies the firing fractionto match the load. It should be appreciated that the present inventionmay be applied to conventional skip fire engine control, dynamic skipfire engine control or other types of engine control, including avariable displacement control system.

The embodiments described above have primarily been described in thecontext of mitigating NVH concerns during skip fire control of anengine. However, it should be appreciated that the described techniquesare equally applicable to multi-charge level or other types of cylinderoutput level modulation engine operation.

When the use of multiple non-zero firing levels is contemplated (e.g.,during multi-level skip fire or multi-charge level operation of anengine), it is often efficient to consider an effective firing fractionwhich correlates to the percentage or fraction of the cylinders thatwould be fired at a high or reference output. For example, if half ofthe cylinders are fired at a cylinder output level of 70% of a fullfiring output and the other half are fired at the full firing outputlevel, then the effective firing fraction would be 85%. In anotherexample, if a quarter of the cylinders are fired at a cylinder outputlevel of 70% of a full firing output, another quarter are fired at thefull firing output level, and the other half are skipped, then theeffective firing fraction would be 42.5%. In yet another example, iftraditional skip fire operation is used (i.e., firing a designatedpercentage of the firing opportunities), then the effective firingfraction may represent the percentage of the cylinders that are actuallyfired. That is the firing fraction and effective firing fraction areequivalent in single level, skip fire operation.

Rather than being limited to making a skip/fire decision for everyfiring opportunity, the firing control system may choose between firingshaving different torque signatures (dynamic multi-charge level engineoperation) or firing opportunities having more than two choices for thetorque signature, e.g. skip/low/high (dynamic multi-level skip fireengine operation). When only two different firing levels are supportedat any time (as is common in multi-charge level engine operation), theNVH mitigation control can be substantially the same as the controldescribed above for skip fire engine operation. When more than twofiring levels are used, the device control may be based on individualfiring decisions (as discussed in the context of some of the embodimentsdescribed above) or on minimum repeating pattern length (as discussed inthe context of the variable spring absorber embodiment described above)or other appropriate characteristic such as engine order or a harmonicthereof, effective firing fraction, etc.

The invention has been described primarily in the context of controllingthe firing of 4-stroke piston engines suitable for use in motorvehicles. However, it should be appreciated that the described skip fireapproaches are very well suited for use in a wide variety of internalcombustion engines. These include engines for virtually any type ofvehicle—including cars, trucks, boats, construction equipment, aircraft,motorcycles, scooters, etc.; and virtually any other application thatinvolves the firing of working chambers and utilizes an internalcombustion engine. The various described approaches work with enginesthat operate under a wide variety of different thermodynamiccycles—including virtually any type of two stroke piston engines, dieselengines, Otto cycle engines, Dual cycle engines, Miller cycle engines,Atkinson cycle engines, Wankel engines, axial engines and other types ofrotary engines, mixed cycle engines (such as dual Otto and dieselengines), radial engines, etc. It is also believed that the describedapproaches will work well with newly developed internal combustionengines regardless of whether they operate utilizing currently known, orlater developed thermodynamic cycles. The described embodiments can beadjusted to work with engines having equally or unequally sized workingchambers.

The described methods and arrangements may also be integrated into ahybrid powertrain where the crankshaft may be driven by a combination ofan internal combustion engine and some auxiliary power source, such asan electric motor. In general, the auxiliary power source may at varioustimes add or subtract torque from the powertrain crankshaft depending onthe control settings. For example, an electric motor may at times beused as an electric generator to store energy from the powertrain in anenergy storage device such as a capacitor or a battery.

Although only a few embodiments of the invention have been described indetail, it should be appreciated that the invention may be implementedin many other forms without departing from the spirit or scope of theinvention. For example, some of the figures illustrate a controller fora noise/reduction device (e.g., an active mount, an ANC system, a flowregulator or flapper valve, etc.) that receives firing information froma firing fraction calculator and/or firing timing determination unit. Itshould be appreciated that the present invention contemplates that thecontroller may receive a wide variety of types of firing informationfrom any suitable source. In some approaches, this means that the firinginformation is received either from a firing fraction calculator or afiring timing determination module, both and/or one or more othermodules or mechanisms. The firing information may be any suitableinformation related to the operation of the working chambers in a skipfire manner and therefore includes, but is not limited to, a firingdecision, a firing sequence, a firing fraction, a firing history for oneor more working chambers, information identifying a particular workingchamber and firing characteristics/operations of that working chamber,etc. Therefore, the present embodiments should be consideredillustrative and not restrictive and the invention is not to be limitedto the details given herein.

What is claimed is:
 1. A method of mitigating or adjusting an NVHcharacteristic of a vehicle having a powertrain that includes an enginecapable of skip fire operation, the engine including a plurality ofworking chambers, the method comprising: operating the engine in a skipfire mode at a first effective displacement; and actively controlling adevice that is not a part of the powertrain in a feed forward manner,during the skip fire operation at the first effective displacement, toalter the NVH characteristic of the vehicle in a desired manner based atleast in part on specific individual skip fire firing decisions, eachspecific individual skip fire firing decision being indicative ofwhether to skip or fire an individual working chamber during a singleassociated skip fire firing opportunity, wherein for each skip firefiring decision, the device is controlled differently during theassociated skip fire firing opportunity based on whether the associatedskip fire firing decision is a skip or a fire, the control of the devicevarying over the course of each engine cycle in accordance with thespecific individual skip fire firing decisions associated with thatengine cycle during the skip fire operation of the engine at the firsteffective displacement.
 2. A method as recited in claim 1 wherein: theactively controlled device includes at least one active engine mounthaving an adjustable stiffness or damping characteristic; and for eachskip fire firing opportunity, setting the stiffness or dampingcharacteristic of the at least one active engine mount differently basedat least in part on whether the associated skip fire firing decision isskip or fire, whereby the stiffness or damping characteristic of the atleast one active engine mount varies over the course of an engine cyclein accordance with the skip fire firing decisions associated with thatengine cycle and is controlled in a manner that mitigates selectedvibrations associated with skip fire operation of the engine at thefirst effective displacement.
 3. A method as recited in claim 1 wherein:each working chamber is configured to operate in a sequence of workingcycles, each working cycle having an associated firing opportunity thatoccurs during an associated combustion stroke; during fired firingopportunities, combustion occurs within the working chamber during thecombustion stroke to thereby create a firing impulse, and during skippedfiring opportunities combustion does not occur within the workingchamber during the combustion stroke such that no firing impulse iscreated during a portion of the combustion stroke of a skipped workingcycle that corresponds to the firing impulse in a fired working cycle,such no firing impulse being referred to as a skipped firing impulse;and actively controlling the device that is not a part of the engine toalter the NVH characteristic of the vehicle during skip fire operationof the engine at the first effective displacement includes, for each ofa set of skipped firing opportunities, generating a correspondingdiscrete sound synchronized with the corresponding skipped firingimpulse.
 4. A method as recited in claim 1 wherein: each working chamberis configured to operate in a sequence of working cycles, each workingcycle having an associated firing opportunity that occurs during anassociated combustion stroke; during fired firing opportunities,combustion occurs within the working chamber during the combustionstroke to thereby create a firing impulse, and during skipped firingopportunities combustion does not occur within the working chamberduring the combustion stroke such that no firing impulse is createdduring a portion of the combustion stroke of a skipped working cyclethat corresponds to the firing impulse in a fired working cycle, such nofiring impulse being referred to as a skipped firing impulse; andactively controlling the device that is not a part of the engine toalter the NVH characteristic of the vehicle during skip fire operationof the engine at the first effective displacement includes, for each ofa set of skipped firing opportunities, generating a correspondingvehicle vibration synchronized with the corresponding skipped firingimpulse.
 5. A method as recited in claim 1 wherein each fired workingcycle has an associated firing impulse, and wherein actuation of thedevice is substantially synchronized with the firing impulse while theengine is operating in the skip fire mode at the first effectivedisplacement.
 6. A method of mitigating or adjusting an NVHcharacteristic of a vehicle having a powertrain that includes an enginecapable of skip fire operation, the engine including a plurality ofworking chambers, the method comprising: operating the engine in a skipfire mode at a first effective displacement; and actively controlling adevice that is not a part of the powertrain in a feed forward manner,during the skip fire operation at the first effective displacement, toalter the NVH characteristic of the vehicle in a desired manner based atleast in part on specific individual skip fire firing decisions, eachspecific individual skip fire firing decision being indicative ofwhether to skip or fire an individual working chamber during a singleassociated skip fire firing opportunity, wherein for each skip firefiring decision, the device is controlled differently during theassociated skip fire firing opportunity based on whether the associatedskip fire firing decision is a skip or a fire, the control of the devicevarying over the course of each engine cycle in accordance with thespecific individual skip fire firing decisions associated with thatengine cycle during the skip fire operation of the engine at the firsteffective displacement, wherein at least two filters are used in theactive control of the device during the skip fire operation of theengine at the first effective displacement to shape the response of thedevice; using a first one of the filters in association with skippedfiring opportunities of the skip fire working chambers that occur duringthe skip fire operation of the engine at the first effectivedisplacement, wherein the first filter is not used in association withfired firing opportunities of the skip fire working chambers that occurduring skip fire operation of the engine at the first effectivedisplacement; and using a second one of the filters in association withfired firing opportunities of the skip fire working chamber that occurduring the skip fire operation of the engine at the first effectivedisplacement, wherein the second filter is not used in association withthe skipped firing opportunities of the skip fire working chamber thatoccur during the skip fire operation of the engine at the firsteffective displacement.
 7. A method of mitigating or adjusting an NVHcharacteristic of a vehicle having a powertrain that includes an engineduring cylinder output level modulation operation of the engine, theengine including a plurality of working chambers, the method comprising:operating the engine in the cylinder output level modulation mode at afirst effective displacement; and actively controlling a device that isnot a part of the powertrain in a feed forward manner, during thecylinder output level modulation operation at the first effectivedisplacement, to alter the NVH characteristic of the vehicle in adesired manner based at least in part on specific individual cylinderoutput level decisions, each specific individual cylinder output leveldecision being indicative of a desired cylinder output level for anassociated cylinder during a single associated firing opportunity,wherein for each cylinder output level decision, the device iscontrolled differently during the associated firing opportunity based onthe associated cylinder output level decision, the control of the devicevarying over the course of each engine cycle in accordance with thespecific individual cylinder output level decisions associated with thatengine cycle during the cylinder output level operation of the engine atthe first effective displacement.
 8. A method as recited in claim 7wherein: the actively controlled device includes at least one activeengine mount having an adjustable stiffness or damping characteristic;and for each firing opportunity, setting the stiffness or dampingcharacteristic of the at least one active engine mount differently basedat least in part on different cylinder output level decisions, wherebythe stiffness or damping characteristic of the at least one activeengine mount varies over the course of an engine cycle in accordancewith the cylinder output level decisions associated with that enginecycle and is controlled in a manner that mitigates selected vibrationsassociated with cylinder output level modulation operation of the engineat the first effective displacement.
 9. A method as recited in claim 7wherein: each working chamber is configured to operate in a sequence ofworking cycles, each working cycle having an associated firingopportunity that occurs during an associated combustion stroke; duringfiring opportunities having a first associated firing level, combustionoccurs within the working chamber during the combustion stroke tothereby create a firing impulse, and during firing opportunities havinga second associated firing level that is different than the first firinglevel, the device that is not a part of the engine is activelycontrolled to generate a corresponding discrete sound that issynchronized with the combustion stroke associated with the firingopportunities having the second associated firing level.
 10. A method asrecited in claim 7 wherein: each working chamber is configured tooperate in a sequence of working cycles, each working cycle having anassociated firing opportunity that occurs during an associatedcombustion stroke; during firing opportunities having a first associatedfiring level, combustion occurs within the working chamber during thecombustion stroke to thereby create a firing impulse, and during firingopportunities having a second associated firing level that is differentthan the first firing level, the device that is not a part of the engineis actively controlled to generate a corresponding vehicle vibrationthat is synchronized with the combustion stroke associated with thefiring opportunities having the second associated firing level.
 11. Amethod as recited in claim 7 wherein each fired working cycle has anassociated firing impulse, and wherein actuation of the device issubstantially synchronized with the firing impulse while the engine isoperating in the cylinder output level modulation mode at the firsteffective displacement.
 12. A method as recited in claim 7 wherein: thecylinder output level modulation mode is a skip fire operating mode inwhich some working cycles are active working cycles that are fueled andfired and some working cycles are skipped working cycles that are notfired; and for each firing opportunity, an independent firing decisionis made whether to skip or fire an individual associated working chamberduring such firing opportunity.
 13. A method as recited in claim 7wherein: the cylinder output level modulation mode is a firing levelmodulation operational mode; and for each firing opportunity, anindependent firing level decision is made that is indicative of a levelat which an individual associated working chamber is to be fired duringsuch firing opportunity.
 14. A method of mitigating or adjusting an NVHcharacteristic of a vehicle having a powertrain that includes an engineduring cylinder output level modulation operation of the engine, theengine including a plurality of working chambers, the method comprising:operating the engine in the cylinder output level modulation mode at afirst effective displacement; and actively controlling a device that isnot a part of the powertrain in a feed forward manner, during thecylinder output level modulation operation at the first effectivedisplacement, to alter the NVH characteristic of the vehicle in adesired manner based at least in part on specific individual cylinderoutput level decisions, each specific individual cylinder output leveldecision being indicative of a desired cylinder output level for anassociated cylinder during a single associated firing opportunity,wherein for each cylinder output level decision, the device iscontrolled differently during the associated firing opportunity based onthe associated cylinder output level decision, the control of the devicevarying over the course of each engine cycle in accordance with thespecific individual cylinder output level decisions associated with thatengine cycle during the cylinder output level operation of the engine atthe first effective displacement, wherein at least two filters are usedin the active control of the device during the cylinder output levelmodulation operation of the engine at the first effective displacementto shape the response of the device; using a first one of the filters inassociation with firing opportunities having a first associated firinglevel that occur during the cylinder output level modulation operationof the engine at the first effective displacement, wherein the firstfilter is not used in association with firing opportunities having asecond associated firing level that occur during the cylinder outputlevel modulation operation of the engine at the first effectivedisplacement; and using a second one of the filters in association withfiring opportunities having the second associated firing level thatoccur during the cylinder output level modulation operation of theengine at the first effective displacement, wherein the second filter isnot used in association with the firing opportunities of having thefirst associated firing level that occur during the cylinder firinglevel modulation operation of the engine at the first effectivedisplacement.
 15. A system for reducing NVH generated by an internalcombustion engine during cylinder output level modulation operation ofthe engine, the internal combustion engine having a plurality of workingchambers and a cylinder output level modulation engine controllerarranged to direct cylinder output level modulation operation of theengine, the system comprising: at least one actuator that is not part ofa powertrain that includes the engine; and a NVH controller arranged toactively control actuation of the at least one actuator in a feedforward manner during cylinder level modulation operation of the engineat a first effective firing fraction to facilitate mitigation of an NVHcharacteristic associated with the cylinder level modulation operationof the engine at the first effective firing fraction, wherein the feedforward control is based at least in part on specific individualcylinder output level decisions, each specific individual cylinderoutput level decision being indicative of a desired cylinder outputlevel for an associated cylinder during a single associated firingopportunity, wherein for each cylinder output level decision, theactuator is controlled differently during the associated firingopportunity based on the associated cylinder output level decision, thecontrol of the actuator varying over the course of each engine cycle inaccordance with the specific individual cylinder output level decisionsassociated with that engine cycle during the cylinder output leveloperation of the engine at the first effective displacement.
 16. Asystem as recited in claim 15 wherein the at least one actuator isselected from the group consisting of: a flow control device, at leastone active engine mount, at least one speaker, at least oneelectromagnetic actuator, at least one shaker and at least one voicecoil motor.
 17. A system as recited in claim 15 wherein the internalcombustion engine is a part of a vehicle having a cabin, and the atleast one actuator includes at least one speaker that serves as theactively controlled actuator and the NVH controller includes an activenoise cancellation controller, the active noise cancellation controllerbeing arranged to drive the at least one speaker in a manner thatmitigates or masks noises associated with cylinder output modulationoperation of the engine.
 18. A system as recited in claim 15 wherein:the at least one actuator includes at least one active engine mount thatserves as the actively controlled actuator, each active engine mounthaving an adjustable stiffness or damping characteristic; and thestiffness or damping characteristic of the at least one active enginemount is controlled in a manner that mitigates selected vibrationsassociated with cylinder output level modulation operation of theinternal combustion engine at the first effective firing fraction.
 19. Asystem as recited in claim 15, wherein the NVH controller includes: avariable filter arranged to shape the response of the actuator duringoperation of the engine at the first effective firing fraction; and afilter coefficient setter arranged to set selected filter coefficientsof the variable filter.
 20. A system as recited in claim 19 wherein theNVH controller is arranged to periodically check the filter coefficientsduring the cylinder output level modulation operation of the engine atthe first effective firing fraction, the periodic checking beingperformed on a firing opportunity by firing opportunity or engine cycleby engine cycle basis.
 21. A system as recited in claim 19, wherein thefilter coefficient setter includes a lookup table that providesappropriate filter coefficients for various skip fire operatingconditions, wherein current engine speed is used as a first index forthe lookup table.
 22. A system as recited in claim 19 wherein the NVHcontroller includes: a plurality of filters arranged to shape theresponse of the actuator, wherein each filter is used in associationwith an associated one of the working chambers during the cylinderoutput level modulation operation of the internal combustion engine atthe first effective firing fraction such that different filters are usedin connection with working chambers during the cylinder output levelmodulation operation of the internal combustion engine at the firsteffective firing fraction.